RFI: pigment in birds' bills etc

This is a rather odd, and doubtless naive enquiry, but it may help to
resolve a (mildly) raging debate among Canberra birdos at present. As you
may know if you look at the Hotline Highlights, a black pelican has been
hanging around Canberra lakes for most of the year. The debate centres
around whether it is 'naturally' black, or oil-stained. The weight of
opinion among observers favours the former, but a knowledgable member has
just tossed in the following plausible argument for the latter.
He argues that since melanin only replaces other pigment AND A BIRD'S BILL
CONTAINS NO PIGMENT, the pelican's black bill is evidence of oil staining.
With that given, he must be right, but is the proviso correct? I find it
hard to accept that a bird's bill has no pigment, in terms of UV protection
if nothing else.
Would someone like to take a minute or two to sort this one out for me/us?
Thanks in anticipation!
Ian
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Ian Fraser, Canberra
Environment Tours; Vertego Environmental Writing Consultancy
ph: 02 62491560 fax: 02 62473227